AC3.3 TradHeli Release Discussion

WARNING to TradHeli users:

Do not attempt to fly AC3.3 until you hear otherwise from me.  I have not even bench tested it yet, let alone test flown it.  There are quite a lot of changes that have gone in that could be crash-o-matic for helicopters.

AC3.3 release for Tradheli is likely to be delayed.

This post will serve as the official release progress thread for TradHeli.

Warning: DO NOT FLY RC6!  It has a critical bug that will likely end in a crash.

Warning for RC5:

RATE_YAW_FILT_HZ param will change defaults from 5Hz to 20Hz to be more suitable for helicopters.  If you have never changed this parameter from 5 before, then it will automatically update the value to 20 without warning.  This much faster filter will probably require reduction in your P and D terms, and the yaw may oscillate badly.  Be prepared to retune these.  As a safety measure, probably cut them in half for your first take-off.

Warning #2 for RC5:

I accidentally broke the Landing Detector.  It will probably never trigger.  You should land in Stabilize mode, or be prepared to shut down the motor as soon as it touches the ground in Alt_Hold, Loiter, Auto, etc.

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Replies

  • Hi,

    I just installed 3.3 rc-8 using MP 1.3.30 and the default values are for RATE_PIT_P=0.020 and RATE_RLL_P=0.020. I for sure never changed these settings (only calibration - no flying yet), but after a while both were on 0.434 instead of 0.020. No other setting was changed.

    • Hi, I did update the default a while ago (before rc8 I'm pretty sure) so if you had left your gains on default, then they would get updated unfortunately.

      Are you saying that the gains increased from 0.020 to 0.434 on their own?

  • For some reason in RC8 the FF Values under extended tuning are grayed out and can not be adjusted.

    Also, what is the difference between RATE_PITCH_VFF and RATE_PITCH_AFF?

    • Yes, this was actually not supposed to go into RC8 but was included because Randy rebased RC8 on Master.  It's a concept I am working on but was not ready for people to see it yet.

      For RC9, the AFF is gone, and VFF will be renamed back to FF so it will not be greyed out anymore.  Sorry about the confusion. 

      Hopefully I'll have this all sorted out for 3.4.  The AFF does help a lot, but unfortunately it's yet another parameter to tune.  I am starting to question the cascading PID controller we currently use, and open to other suggestions if anybody has others.  There has got to be a better way.

      • Rob,

          I have just started using a Pixhawk for a unique helicopter project in which it has two forward facing tailrotors rather than a traditional tailrotor.  Benefit is that you can use them for directional control and forward thrust.  I'm slowly learning the copter code and I was surprised that their is no direct link to longitudinal and lateral cyclic.  It appears it is all errors from desired rate, attitude, etc.  As it seems you are all aware, feedback in rate can be catastrophic.  This is true of even the manned helicopters and they design around this instability using notch filters for the calculated frequency.  If you were to start over with the control laws, I would recommend follow more manned helicopter control laws where base control laws are passing through the commanded controls and then feeding back rate and attitude to modify the control and obtain the desired control strategy (ie. rate command or attitude command).  What exactly do the RATE_RLL_FF and RATE_PIT_FF parameters do?  This pic is the flybarred version of it.  I just upgraded the head to a 4 bladed head.3702723880?profile=original

        • Hi Bill,

          can you please provide any data regarding efficiency in hover and forward flight in relation to the tradional design ?

          • This design is used by full scale manufacturers to achieve high speed forward flight. This design, for full scale helicopter, is limited by the advancing rotor tip speed going supersonic and retreating blade stall. For RC aircraft I'll primarily be concerned with retreating blade stall.
            As far as efficiency or performance considerations, there are not any benefits in this design for the hover/low airspeed regime. In fact, there will probably be a 3-5% increase in power required due to the second tail rotor. In the forward flight regime, the benefit comes from not having to pull more collective and tilt the vehicle more forward to achieve high speeds. Collective can be set just to provide enough lift to offset weight and forward facing tail rotors pull aircraft thru the air. And cabin attitude can be kept at optimum to reduce drag. Plus if there is a short wing, the rotor thrust can be reduced. I don't have any data on the benefits full scale manufacturers have seen but for them they would not even be able to achieve those speeds without this configuration or some way to overcome the limitations of helicopter high speed flight.
    • Rob on 25.5.2015 is mentioning that he has added a Yaw Acceleration FF.

      I guess that RATE_PITCH_AFF means RATE_PITCH Acceleration Feed Forward.

      Because I have the same questions but have not found more INFO yet.

      • I finally found out. Yes, it is acceleration FF and only applies to the yaw for right now. the pitch and roll AFF currently do nothing. It's a parameter rob is playing around with.

        My biggest complaint with Traditional Heli so far is the lack of communication with many of these features and the severely outdated wiki for traditional heli. 

        As I learn more about it I will gladly help update some of it. I'm looking forward to testing soon though!

  • Any updates on the earth frame issues? Has this been resolved with Arducopter 3.3 so Acro mode is proper now, or, can you still not do flips?

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